Monocular 3D Measurement in Featureless Elongated Structures Using Light-Section Method and Active Laser-Based SfM

When measuring large, elongated structures such as tunnels, the integration of the local three-dimensional (3D) shapes measured at multiple points using tools such as laser scanners is necessary. However, because tunnel interiors often have smooth, texture-less surfaces, estimating the relative pose between measurement points is difficult. This paper proposes a lightweight 3D measurement method using a single camera and laser projection. The system performs cross-sectional shape measurements using the light-section method and pose estimation using the projected laser features. By introducing a scale optimization approach that minimizes the nearest-neighbor distances between point clouds, accurate global 3D reconstruction is achieved without relying on external sensors. The proposed method enables efficient and precise measurements, even in featureless environments.